Deflagrating propellant explosives, such as blackpowder and smokeless powders, which generate a large volume of hot gas when burnt, and produce it very rapidly when under such confinement as is provided by a gun barrel, have been used for many centuries as the means of projecting bullets, cannon balls and shells. High explosives, developed during the nineteenth century, provide the means of projecting metal objects without the need for a barrel since, upon detonation, they evolve gas so quickly that extremely high pressures can be generated without any confinement. The rate of decomposition is known as the “detonation velocity” and corresponds approximately to the velocity of sound in the undetonated material.
The fragments of the body of a modern artillery shell are projected by the gases generated by the detonation of high explosives. In this case the confinement of the explosive afforded by the steel body is of less importance than the velocity of detonation of the explosive even without such confinement and the velocity at which the metal fragments are projected depends only slightly upon the confinement. Thus a plate of steel, for example six millimetres thick and applied to the surface of a sheet of high explosive of twice this thickness, might be projected at a velocity of about 0.7 km/sec upon detonation of the explosive. Sandwiching the explosive between two such plates will increase the velocity of the plates to about a kilometre a second by delaying the effluence of the high pressure detonation products and thus maintaining the pressure for longer. This means of enhancing a charge of high explosive is known as “tamping”.
In practice such metal plates tend to disintegrate in flight, their integrity being destroyed by the divergent detonation wave and by internally reflected shock waves, although the interposing of a layer of inert buffering material between the explosive and the metal helps to reduce this tendency to break up.
A great advance was made in the usefulness of a thin layer of metal in contact with detonating high explosive with the invention, during the Second World War, of the “shaped charge”. In its most commonly encountered form, this consists of a generally cylindrical or conical block of explosive which has the means of initiating a detonation at one end and a conical cavity, of which the base extends substantially across the other end, at the other. This conical cavity is lined by a hollow cone of metal, typically copper, with a wall thickness of one or two millimeters.
Detonation of the explosive causes a wave of extremely high pressure to pass along the outside of the metal cone, advancing from its apex to its base, collapsing it as it goes. This causes an evertion of the inner surface of the metallic cone which is formed into a highly elongated rod along the axis of rotation of the assembly. This is known as the “jet” and it is possessed of a velocity gradient along its length, with the tip travelling significantly faster than the tail. This difference in velocity causes the jet to stretch until it breaks up into short fragments which begin to tumble after it has travelled a distance equivalent to a few charge diameters. So high is the velocity of such a jet that it is able to penetrate the hardest and toughest of armour to a depth equivalent to several charge diameters. The main applications of such charges is the attack and perforation of the sides of armoured vehicles and the “stimulation” of oil wells. In another form of shaped charge the explosive and the metal-lined cavity are essentially linear rather than radially symmetrical with a typically V-sectioned, metal lined, groove formed in the explosive. Such charges are less penetrating than radially symmetrical shaped charges but they make elongate cuts in the target. They are most used for the cutting rather than perforation of targets.
A second form of metal-projecting high explosive charge is the “explosively formed projectile” or EFP. This is similar to the jet-forming shaped charge except that the metal liner is either in the form of a cone of so wide an angle that it produces no jet, or of a shallow dish. Such projectiles are deformed to greater or lesser degrees and take shapes varying from shallow dishes of only slightly smaller diameter to the unformed projectile to rods with explosively forged tail fins or cones. Simple versions of such charges constitute many of the improvised stand-off weapons used to attack passing armoured vehicles and commonly referred to as “a category of roadside bomb”.
Gun barrel technology has been used since the 1980's for the projection of water at high velocity (about 350 m/s) for the purpose of breaking up improvised bombs without causing the detonation of the explosive which they contain. Water as a projectile for this purpose has the advantages of great dispersive power of the bomb components, a high specific heat and great wetting ability, which tend to quench incipient deflagration, and, compared with metals, a low density, which decreases the probability of initiating sympathetic detonation of the target explosive.
The velocity at which projectiles can be shot from gun barrels is subject to the law of diminishing returns in that the power and size of a gun has to be increased disproportionately in order to attain a modest increase in projectile velocity. This means that disruptors based upon gun barrel technology can be readily defeated by constructing a bomb using a moderately robust case or simply a case of sufficient volume to absorb the energy of the bursting water projectile.
Previous inventions of one of the authors (SCA) had as their purpose the generation of jets of water, of aqueous solutions, or of other liquids, using detonating explosives. These devices used modified shaped charge technology. In one family of such charges the metal liner of conventional radially symmetrical or linear shaped charges was replaced by a liner of liquid: in another the cavity in the explosive was largely or completely filled with liquid. These jets of water achieved velocities several times higher than those generated by propellant explosives fired in gun barrels; they also had the concomitant advantages of much lower weight and much lower cost. The velocity of such jets could, moreover, be largely determined by the ratio of explosive to projected liquid. Of particular value are versions of such charges in which both explosive and projected liquid are loaded into flask-like plastics housings by the operator since this enables the amount of explosive used and the ratio of explosive to projected fluid to be determined by the operator. Acquisition, transportation and storage of the empty plastics vessels is also independent of regulations pertaining to explosive-filled devices.
It will be understood that all of these devices required the imparting of particular shapes to the explosive charge since it is the carefully contrived concavity of the explosive itself which determines the direction in which the projectile fluid is projected. U.S. Pat. No. 6,269,725 teaches the construction of a “fluid-filled bomb-disrupting apparatus” known as the “Hydra-Jet” which uses a square-sectioned plastics jar in which the explosive element consists of two rectangular sheets of explosive, contiguous along one edge of each, with an adjustable angle between the two. The explosive element is immersed in water contained in the jar with the mid-line plane between the two sheets of explosive passing through the vertical mid-line of one side of the jar. Upon detonation, a linear jet of water is projected outwards in this plane.
According to a first aspect of the present invention there is provided a liquid-jacketed disrupter comprising a container for receiving liquid and housing a receptacle for explosive material, in which the container comprises one or more indentations which result in the generation of liquid jets upon detonation.
The container may be generally cylindrical.
The or each indentation may be a concavity. For example, the or each indentation may be arcoid in transverse section.
The radius of curvature of the concavity may be substantially the same as adjacent convex surfaces of the container.
There may be two or more indentations.
The indentation may comprise a groove, dimple or the like, for example a longitudinal groove in the container wall.
One object of the invention is the generation of jets of liquid travelling at high velocity using energy derived from the detonation of elements of high explosive. Another object is to use elements of high explosive which have such simple shapes as may be easily confected by the operator in the field. Such explosive elements might thus consist of one or more lengths of detonating cord or of a thin-walled plastics tube into which the operator tamps plastic explosive. Directionality of part or parts of the explosively projected water is imparted by particular shaping of the container of the projected liquid rather than of the explosive.
According to a second aspect of the present invention there is provided a liquid-jacketed disrupter comprising a container for receiving liquid and housing a receptacle for explosive material, in which the receptacle comprises an interchangeable cartridge such that cartridges with different volumes can be used in conjunction with the container.
The disrupter may be provided in combination with a set of two or more cartridges having different volumes which can be selectively received in the container.
The container and receptacle may be provided with co-operating formations for securely retaining the receptacle. The formations may comprise screw thread formations.
Aspects of the present invention may be provided in the same disrupter.
The Invention comprises or consists of a vessel of liquid, which is most commonly water or a mixture of water with a substance capable of lowering the freezing point of the water, and a mass of explosive situated within this body of liquid. The shape of the explosive element may be compact, such as an approximation to a sphere or elongate, consisting of a strip of explosive with or without an internal stiffening component such as a plastics rod, or an external stiffening and shaping element such as a plastics tube. It may conveniently comprises, or consist of, one or more strands of detonating cord. The explosive element, of whatever shape, is not provided with any significant indentations or folds.
The vessel containing the liquid, in which the explosive element is immersed, is conveniently made from plastics and may, in the case of an approximately spherical mass of explosive, be itself approximately spherical and be provided with one or more indentations. If the Invention is confected using a generally rod-like explosive element, then the liquid-containing vessel may be generally cylindrical or prismatic with the explosive situated along, or parallel to, the long axis of the vessel. At one or more positions in the wall of the plastics vessel a longitudinal groove is formed. Alternatively, generally round indentations may be formed in the wall of the vessel at one or more places.
When the explosive is detonated, the expanding shockwave which it generates impels the liquid elements close to the indentations or grooves radially outwards and forms them into jets which travel at a higher velocity than that part of the liquid not adjacent to an indentation or groove.